This invention relates generally to tripot joints.
Typical tripot joints include a tripot housing that is fixed at one end to a shaft and open at its opposite end to receive a tripot spider into the housing which is fixed to another shaft. The spider has three trunnions which project radially outwardly into three respective longitudinal guide channels of the housing. Each trunnion carries a ball assembly which rollably guides the trunnions along the channels. This type of joint enables torque to be transmitted between the shafts at an angle and further enables a certain amount of axial plunging movement of the spider within the housing during operation of the joint to accommodate adjustment in the effective length of the shafts. A typical application for such joints is in front wheel drive applications for automotive vehicles, where the joint forms part of a shaft assembly operative to transmit torque from the transmission to the front drive wheels, while allowing for effective changes in the axial length of the shaft assembly through plunging of the tripot joint to accommodate up and down movements of the drive wheels.
The complex motion of such tripot joints make them susceptible to noise, shudder, and/or chattering. The shaft angle and rotation of the joint during the transmission of torque, coupled with axial plunging of the spider within the housing, presents a challenge to design such joints so that the ball assemblies to run true in the guide channels of the housing, attributing at least in part to the noise, chatter and/or shudder problems.
One particular type of tripot joint shown to perform exceptionally well is manufactured by the assignee of the present invention. It employs a multi-part ball assembly on each trunnion that includes an inner ball formed with a part-spherical inner concave surface that mates with a part-spherical convex surface of the respective trunnions and supports an outer roller or ball on a complement of needle rollers which support the outer ball for rotation relative to the inner ball, and enable the inner ball, and thus the trunnions, to shift or slide axially of the outer ball when transmitting torque through the joint at an angle in order to maintain the outer balls riding in their respective guide channels of the housing.
Typically, the outer ball has bearing retainers adjacent its axial ends which serve to capture the bearings in the axial direction. The retainers stop short of extending into the path of the inner ball in order that the inner ball is able to slide axially beyond the ends of the rollers. Thus, there is nothing retaining the inner ball against axial separation from the outer ball before the ball assemblies are mounted on the trunnions and disposed within the guide channels of the housing. As such, the ball assemblies are subject to inadvertent disassembly and must be carefully handled during the manufacture and service of the tripot joint or else the ball assembly can fall apart under its own weight. Once the inner ball is separated from the outer ball, the complement of needle rollers are prone to falling inwardly and becoming separated from the outer ball, further adding to the handling difficulties.
It is an object of the present invention to eliminate or greatly minimize the foregoing limitations of prior tripot joints while maintaining their high performance.
A tripot joint assembly constructed according to the present invention includes a tripot housing coupled to a first shaft and having three axially extending ball channels, and a tripot spider coupled to a second shaft and having three radially outwardly extending trunions which are disposed in the guide channels and each presenting a convexly curved outer surface. A ball assembly is disposed on each trunion and includes an inner ball having an inner concavely curved surface mating with the convexly curved surface of each trunion to establish a rotatable and angular support of each inner ball on its respective trunion. The ball assemblies each include an outer ball having a convexly curved outer surface rollably engaging the guide channels of the housing and an inner surface spaced radially from an outer surface of the inner ball. Each ball assembly further includes a complement of roller elements disposed between the inner and outer balls and providing rolling support of the outer balls on the inner balls, and axial sliding support of the inner balls on the outer balls. According to the invention, at least one yieldable retainer is mounted on each outer ball and projects radially inwardly into the axial sliding paths of the inner balls in at least partial overlapping relation to the inner balls. The retainers present yieldable impediments along the axial sliding paths that are operative to yield out of the axial sliding paths during operation of the joint in response to application of an axial sliding force on the retainers exceeding a pre-determined yield force of the retainers to permit axial movement of the inner balls along the outer balls beyond the retainers. The retainers are further operative to restrain the outer balls against axial separation from the inner balls prior to disposing the ball assemblies within the guide channels.
The invention has the advantage of simplifying the manufacture and assembly of tripot joint assemblies, particularly with respect to the ball assemblies.
The ball assemblies, fitted with the yieldable retainers, enable the ball assemblies to be pre-manufactured and assembled as self-contained ball modules that remain assembled prior to being united with the trunions and ball guides.
The invention has the further advantage of providing a yieldable retainer that, when the ball assemblies are mounted on the trunions and disposed in the ball guides, yield out of the way during normal joint operation to permit the inner ball to slide axially relative to the outer ball beyond the retainers. As such, the invention provides the advantageous assembly benefits without impairing the operation of the joint.
The invention has the further advantage of providing the subject yieldable retention of the inner ball without having to increase the radial size of the joint, which would be necessary if rigid, non-yieldable retainers were employed in overlapping relation to the inner ball, but with sufficient clearance to accommodate full axial sliding travel of the inner ball relative to the outer ball during normal operation of the joint. The yieldable retainer, extended into the axial path, is effective to capture the inner ball prior to assembly, yet yields out of the way during normal operation to accommodate full axial travel of the inner ball relative to the outer ball in a relatively smaller package size.
The invention has the further advantage of being readily adaptable to existing and new tripot product applications.
According to a further aspect of the invention, the yieldable retainer is one that is elastically deformable such that the retainer returns to the axial sliding path once the inner ball slides axially inwardly of a retainer. Such restoration of the yieldable retainer facilitates servicing of the tripot joint by maintaining axial retention of the inner ball relative to the outer ball as a self-supporting ball module upon removal of the ball assemblies from the ball channels and trunnions.